(1) Field of the Invention
This invention relates to a thin film magnetic head to be used in a magnetic recording device, and more particularly to a thin film magnetic head with an improved reliability achieved by reducing to a lower level the magnitude of "undershoot" that appears on both sides of a main peak of the waveform of the reproduced data signal.
(2) Description of the Related Art
A magnetic recording device comprises as essential components thereof a magnetic recording medium for storing data that is mainly made of a hard magnetic thin film and a magnetic head for recording data into and reproducing them from the magnetic recording medium. Because of the recent technological development for high density data storage, the thin film magnetic head has been remarkably improved in terms of not only data recording density but also the data recording frequency. Currently, thin film magnetic heads having a low inductance and a high signal reproducing efficiency are generally used to realize a high data recording density. A thin film magnetic head comprises a pair of magnetic poles with a gap disposed therebetween, which magnetic poles are made of respective thin films having a thickness of several micrometers.
A first known thin film magnetic head is shown in FIGS. 1A and 1B of the accompanying drawings, of which FIG. 1A illustrates a schematic sectional view of the head, and FIG. 1B illustrates an output waveform of a reproduced signal.
As shown, in this known thin film magnetic head comprises first and second magnetic pole layers 100 and 102 that are connected to each other at the respective base sections 100d and 102d and are made of thin film soft magnetic materials, a thin film coil 103 wound at least around either the first magnetic pole layer 100 or the second magnetic pole layer 102 and a magnetic gap layer 104 disposed between the front end sections 100a and 102a of the first and second magnetic pole layers 100 and 102.
As shown, an isolated transition of magnetization 112 is formed to separate opposite magnetizing directions 108 and 110 of a recording medium 106 disposed under the magnetic head. When the recording medium moves along arrow 113, the data signal reproduced by the thin film magnetic head shows a waveform having an isolated main peak 114 representing the reproduced data signal and two undershoots 116 located respectively on lateral sides of the main peak 114 and produced respectively corresponding to a lateral section 100b of the first magnetic pole layer 100 and a lateral section 102b of the second magnetic pole layer 102.
The undershoot output 116 located on the respective lateral sides of the isolated main peak 114 have a polarity opposite to that of the isolated main peak 114 and interferes with the isolated main peak 114 to change the value of the isolated main peak 114 as the recording linear density of the recording medium increases and the distance separated by the isolated transition of magnetization 112 is reduced. Additionally, the isolated main peak 114 can eventually be caused to be shifted.
The undershoot outputs 116 appear when the isolated transition of magnetization 112 of the recording medium 106 passes by the lateral section 100b and goes under the first magnetic pole layer 100 and when it passes by the lateral section 102b and leaves the second magnetic pole layer 102, and this is because the rate at which the magnetic flux generated by the isolated transition of magnetization 112 flows into the first magnetic pole layer 100 and the second magnetic pole layer 102 changes abruptly at those respective points.
A second known thin film magnetic head is proposed in IEEE Transactions on Magnetics, Vol. 29, No. 6., pp. 3837-3839 (Nov. 1993) to reduce the undershoots 116 having the polarity opposite to that of the isolated main peak 114. FIGS. 2A and 2B of the accompanying drawings illustrate the proposed magnetic head. FIG. 2A shows an enlarged schematic partial sectional view of the head and FIG. 2B shows the output waveform of a reproduced signal. Here, the components that are same or similar to their counterparts of the magnetic head of FIGS. 1A and 1B are denoted respectively by the same reference symbols.
The second known thin film magnetic head is provided on the front end sections 100a and 102a of the first and second magnetic pole layers 100 and 102 with recesses 100c and 102c. These recesses 100c and 102c are formed by partly removing the respective front end sections 100a and 102a by means of an appropriate technique such as ion etching or ion milling. As a result, the undershoots 118 have an amplitude slightly smaller than that of the undershoots of the first known magnetic head.
However, the above described second known thin film magnetic head is accompanied by the following problems.
(1) While the undershoot outputs 118 have a low profile, they are still there. As described above, the undershoots result in shifting of the isolated main peak and hence raising the detection error rate in the peak detecting operation conducted when the magnetic recording device is operating for data reproduction.
(2) As the front end sections 100a and 102a are partly removed, they are made partly very thin on the respective sides of the magnetic gap 104. Then, a magnetically saturated state appears in the front end sections 100a and 102a when an electric current flows therethrough for data recording operation so that the transition of magnetization 112 is broadened resulting in the reduction of the output level for high density data recording.
(3) Because of the recessed profile of the front end sections 100c and 102c, dust and other contaminants can easily be caught there to consequently reduce the reliability of the magnetic recording device comprising such a thin film magnetic head.
(4) In order to form recesses in the front end sections 100a and 102a, their forming process must be carried out from the side that is to be magnetically floated. More specifically, after slicing a wafer into rows to be worked with a slider for preparing thin film magnetic heads, each of the rows is exposed to light and subjected to an intricate processing operation typically involving ion milling to produce recesses 100c and 102c. Thus, wafers cannot be treated on a mass production basis and the productivity of preparing such recesses is inevitably low.